arch/s390/include/asm/kvm_host.h includes linux/kvm_host.h, but
linux/kvm_host.h includes asm/kvm_host.h .
It turns out that arch/s390/include/asm/kvm_host.h only needs
linux/kvm_types.h, which it already includes.
Stop including linux/kvm_host.h from arch/s390/include/asm/kvm_host.h .
Due to the #ifdef guards, the code works as it is today, but it's ugly
and it will get in the way of future patches.